Lack of melatonin effect on hydrogen peroxide induced bronchoconstriction in isolated and perfused rat lung

effect of melatonin on hydrogen peroxide- induced broncho-and vasoconstrion was examined in vivo in the model of the isolated, perfused and ventilated lung. The administration of hydrogen peroxide (500 mu M) to the perfusate caused a marked decrease in lung compliance, conductance and flow rate. The administration of melatonin (500 mu M) to the perfusate 20 min before and during the hydroperoxide exposure did not cause any change in lung function . Exposure of lung microsomes to hydrogen peroxide (1-100 mu M) did not ind uce any significant increase in malonaldehyde (MDA), an index of lipid pero xidation, and it was not affected by treatment with melatonin (500 mu M) On the other hand, brain microsomes exposed to hydrogen peroxide (1-100 mu M) give rise to increased levels of MDA, which were decreased by pre-treatmen t with melatonin (500 mu M). The results suggest that melatonin may exert a n antioxidant effect in conditions were lipid peroxidation is occurring. It s use may not be relevant in conditions where the mechanisms of the reactiv e oxygen species damage appears to be lipid peroxidation independent, such as the case of hydrogen peroxide induced broncho- and vasoconstriction. (C) 2000 Elsevier Science Inc.